broth dilution method macro broth dilution method A method to determine the minimum inhibitory concentration (MIC) of antibiotics in which growth media is pipetted into a multi-well plate. Each well contains a known concentration of drug which is inoculated with a known quantity of bacteria. The plate is incubated for a specified period of time and each well is assessed for bacterial cell growth. The drug concentration in the first well showing no growth is known as the MIC for that antibiotic. Minimum 2 mL total broth dilution volume.